<!doctype html> 
<html> 
<head> 
    <meta charset="utf-8"> 
    <title></title> 
</head>
<body>

<script type="text/javascript">
	
var a = document.body;
//
var b = a;
b.index = 1;
alert(a.index);
b.style.background = 'black';
</script>
</body>
</html>